During a fire, the occupants of a building may only have a few minutes to escape without harm. Due to the potentially small escape time, it is imperative to give ample warning to the occupants of a burning building. Most devices sold by the fire safety industry rely on audible alarms to alert the occupants in a residential building. Unfortunately, these devices do not help the hearing impaired. Thus, a need arises for a device that provides ample protection for the hearing-impaired in case of a fire emergency.
When it comes to meeting the general public's need for adequate fire emergency notification devices, one is forced to consider whether the standard off-the-shelf audible smoke detector provides the most appropriate stimulus to prompt a person to begin the egress process. It is estimated that 17% of Americans over the age of 18 have some form of hearing loss (35 million people), and over 3% of those people are severely hearing impaired or profoundly deaf [Lucas, 2004]. Hence, a large number of Americans are at a disadvantage for receiving notification of a fire in their residence by the standard audible smoke detector, and the number of people around the world at this disadvantage is even larger.
Waking persons from sleep is of significant importance because the majority of fire deaths in residential settings occur between the sleeping hours of 11:00 pm and 6:00 am. Although only 20% of fires are reported to have taken place during this temporal window, nearly 50% of fire fatalities occur during this time [Ahrens, 2003].
Recent legislation, such as the Americans with Disabilities Act (ADA), has recognized the disadvantage that deaf and hard-of-hearing people have concerning notification by audible fire alarms. As a result, many automatic fire detection systems are now required to signify with an audible alert accompanied by a strobe to provide a visual indication of fire alarm activation.
Known in the art are devices that use visual signals to alert the hearing-impaired of a fire emergency. Examples of such devices are described in U.S. Pat. Nos. 4,227,191 and 4,287,509. These devices combine a detector and a visual alarm in a single device. Another visual warning device is disclosed in U.S. Pat. No. 5,012,223. This device detects the sound from a remote smoke detector and activates a light in response thereto. Visual alarm devices such as these suffer from the serious drawback of being largely ineffective in alerting a hearing-impaired individual who is asleep.
Systems combining tactile stimulation (e.g., vibrators and bed shakers) have been proposed to address this need. One such device is described in U.S. Pat. No. 4,380,759. This device includes a vibration sensor that is placed next to a smoke detector. When the smoke detector activates, the vibration from the audible alarm triggers a vibrating reed that causes a mild sensation on the skin. Devices such as this are cumbersome to use (especially when the device will only be used at a location temporarily, as in a hotel room) as the user must place the transmitting unit in physical contact with the smoke detector, which is often on a ceiling or otherwise difficult to reach. Other devices for the hearing impaired (e.g., the device disclosed in U.S. Pat. No. 5,917,420) involve the transmission of signals from a detector to a furniture shaker or other tactile stimulation device. Devices such as these are usually quite expensive and require special hardware. U.S. Pat. No. 5,651,070 describes a warning device that “listens” for sounds made by devices such as doorbells and smoke detectors and activates a tactile stimulation device in the form of a wrist-watch. This device records a desired audio alarm and continually compares the recorded alarm to ambient sounds picked up from a microphone. This device is burdensome to use in that it requires the user to record the desired sound prior to use. This can be a problem, for example, when a person enters a hotel room late at night because activation of the smoke detector alarm for the purpose of making the recording may disturb other guests.
To address the above-discussed problems with devices such as these, the assignee of the present application has proposed a system described in co-pending U.S. patent application Ser. No. 10/676,779, filed Oct. 2, 2003 and entitled “Method and Apparatus of for Indicating Activation of a Smoke Detector Alarm,” the contents of which are hereby incorporated by reference herein. This system detects a temporal pattern associated with an audible smoke alarm and, upon detection, activates a tactile device such as a bed shaker to wake a person.
While this system has proven very effective, testing of the system with a standard, constantly vibrating bed shaker as the tactile device has revealed that the system was effective in only 76% of the hard of hearing subjects and in only approximately 92% of the deaf subjects. In contrast, hearing able subjects awoke to the bed shaker with constant vibration close to 95% of the time. The lack of response of the hard of hearing and deaf subjects may be due to their conditioned response to the bed shaker as a non-emergency alarm.
The standard audible smoke detector, the emergency alerting system recommended by the fire community, was proven to be effective in awakening 58% of the hard of hearing population and 0% of the deaf subjects. The weighted average effectiveness per hearing level for the U.S. population was found to be 84%. The visual alerting device which is the recommendation by the fire safety community for the hearing impaired population was found to be effective only 35% of the time for the hearing impaired and 60% for the deaf subjects. The visual alerting device had an effective awakening of less than 35% for the hearing able population and a weighted average effectiveness across all hearing levels of 35%. Although the results reported above are over a small statistical sample, they are nonetheless believed to be representative of the results that would be obtained over a larger sample.
The standard audible smoke detector, which is installed in most homes throughout the United States, was found to be only 84% effective across all hearing populations when weighted across the US population on the basis of hearing ability. This means that of the 204 million Americans over 18, thirty-two million might not awaken to the standard audible detector. Many smoke detector manufacturers have already come to accept this reality and now include a statement in their mounting instructions pertaining to the fact that a properly powered activated audible alarm may not be able to awaken a sleeper even when installed to meet the 85 dB at 10 feet or 15 db above ambient NFPA 72 requirements.
A low frequency audible horn, 400–500 Hz and approximately 85 dB, was tested with thirty-six persons of varying hearing ability. Of the five subjects with no hearing loss, all were awakened by the low frequency audible horn. Of the partially hearing subjects, 92% were awakening by the low frequency horn, 35% more frequently than with the standard audible horn. Of the fully deaf subjects, 11% awoke to the low frequency horn. The low frequency horn effectively awakened a larger percentage of subjects, regardless of hearing ability, than the standard audible horn.
What is needed is a more effective method of waking deaf and hard of hearing subjects.